Assembly and method for the mounting of the foot of a blade of a turbine, blower, compressor, and turbine comprising such an assembly

ABSTRACT

The invention relates to an assembly for the mounting of the foot ( 121 ) of a blade, fixed or movable, of a turbomachine, made of metal, in the aperture ( 101 ) of a support made of metal, such as a casing, a fixed flange or the disk ( 10 ) of a rotor.  
     Characteristically, this assembly comprises, between the foot ( 121 ) and the aperture ( 101 ), a non-metallic film ( 20 ), coated or impregnated with an adhesive, in particular a fabric of glass fibres and/or polyamide fibres, advantageously comprising polytetrafluoroethylene.  
     Application for the mounting of blades ( 12 ) of the fan on the disk ( 10 ) of the rotor, or for the fixed and/or movable blades of a compressor, in particular a low-pressure compressor.

The invention relates to a method for the mounting of the foot of a blade of a turbine, made of metal, fixed or movable, in the aperture of a support made of metal, and to the assembly for such a mounting.

Traditionally, provision is made for the surfaces of the feet of the blades of blowers made of metal, in particular of titanium, to be treated. The contact between the bearing surface of the foot of the blade and the flank of the aperture (or slot) of the disk of the fan which accommodates these feet is in fact subjected to multiple forces, which can engender damage to these parts, or even the premature breakage of the components which are in contact.

The present invention is not limited to situations in which the support of the foot of the blade comprises a rotor disk of a fan, but equally encompasses other situations of the mounting of movable blades, for example on the rotor disk of a low-pressure compressor, or even in the intake area of a high-pressure compressor.

Likewise, the present invention relates to the situation in which the support is a casing or a flange supporting fixed blades.

In the areas of contact between the foot of the blade and the aperture accommodating this foot, various types of stresses are incurred.

In particular, the phenomenon referred to as “fretting” is encountered, i.e. contact wear, which is the consequence of repeated rubbing of one component on another, the resultant friction forces engendering damage to the materials due to different fatigue processes. This phenomenon is particularly appreciable in cases of contact between two components made of titanium.

These areas are, therefore, subject to a considerable tendency to damage to the material, as well as to wear of the bearing surfaces of the foot of the blade, which are the areas in contact with the wall of the aperture, and even deformation of these contact areas.

In addition to this, the level of local stresses is very high due to the friction coefficient at the interface between the walls in contact with the foot of the blade and the aperture, derived from metal-on-metal contact.

To resolve these problems, attempts have been made in particular to increase the resistance to wear of the surfaces in contact, and to reduce the friction coefficient.

To do this, in general a surface coating is deposited on the foot of the blade, in the form of a metallic alloy which is resistant to fretting, particularly by plasma projection, or use can be made of a protection element formed from one or more metallic foils (or tinsels), possibly themselves coated, surrounding the foot of the blade, these protection elements possibly being associated with lubricating varnishes.

With this type of solution, the friction coefficient can be reduced to a value generally greater than 0.2. During operation, however, this value regularly increases up to about 0.5, or even beyond if the wear is complete.

For example, the document U.S. Pat. No. 5,160,243 proposes making recourse to an arrangement with a metallic foil between a blade and a disk, both of them being of titanium.

Such processes allow for fretting and wear behaviour to be improved. On the other hand, the implementation of these solutions is relatively laborious, both during the initial mounting as well as when localised repairs are made. In both cases it is in fact necessary to treat the entire bearing surface of the support of the foot of the blade, which incurs lengthy and expensive operations. In addition, when the replacement of a coating is required, it is necessary to implement a long, complex, and relatively aggressive procedure (use of acid and/or mechanical stripper) which is capable of removing the material constituting the surface of the substrate, the substrate possibly being damaged particularly due to a change of surfaces and/or dimensions.

One object of the invention is to provide another method of mounting a turbine blade, fixed or movable, made of metal, in the aperture of a support made of metal, in order to improve both the resistance to contact pressure between these components, while still allowing for very simple and rapid implementation of this procedure, both during initial mounting as well as when repairing the mounting of the blade foot.

According to the invention, this object is achieved by a method of mounting the foot of a turbine blade made of metal, fixed or movable, characterised in that it comprises the following steps:

-   a) Arranged between the foot and the aperture is a non-metallic film     comprising polyamide, coated or impregnated with a polymer adhesive;     and -   b) The adhesive must be applied in such a way that the film adheres     to the foot of the blade and/or to the surface of the aperture.

In this case, it is understood that the film replaces the wear-resistant metallic coating of the prior art.

It has in fact been ascertained that the use of such a non-metallic film, chosen for its wear resistance properties, placed between two metallic components, for example directly on the foot of the blade and therefore coming in contact with the surface of the support aperture, allows for the friction coefficient to be reduced in the contact areas, and therefore for the mounting wear of the foot of the blade to be significantly reduced, so increasing the service life of this connection without impairing its mechanical behaviour before it becomes necessary to resort to making a repair.

This type of film is already being used for the mounting of the feet of blades made of composite material, using a film of the type derived from resistant fibre fabric impregnated with resin.

However, according to the invention, this type of solution is now proposed for metallic blade feet, particularly made of titanium, with entirely satisfactory results.

Clearly, the use of such a non-metallic film in the mounting between the apertures and the blade feet is only possible in the areas of a turbine which are referred to as being cold.

In addition to this, it is appropriate to note that the placement of such a film is remarkably simpler than the depositing of a metallic coating, carried out, for example, by the plasma depositing technique.

Moreover, when the requirement is for the repair of the wear surface of the blade foot, the removal in whole or in part of the film is carried out in an essentially simple manner, by straightforward peeling with the aid of a scalpel. The application and fixing of the new replacement film are themselves also carried out much more simply and rapidly than for a metallic cladding, without the need for technologically complex equipment and without the risk of damaging the support.

Accordingly, the method according to the invention can be used both during the initial mounting as well as when carrying out a repair to the mounting between the foot of a blade and its aperture when this mounting has been initially carried out in accordance with the invention or if recourse has been made to a wear-resistant metallic coating.

Advantageously, the film is provided beforehand with bonding agent, on the surface or throughout its substance.

Preferably, the bonding agent is thermo-polymerisable, and in the course of step b) the assembly comprising at least the foot of the blade, the support, and the film, is placed in an autoclave brought to a temperature which will allow the bonding agent to take, over a predetermined minimum period of time.

According to a variant embodiment of the method according to the invention, during step a) the foot of the blade is clad with a metallic foil, said wear-resistant film then being arranged between the foil and the aperture.

The invention also relates to an assembly for the mounting of the foot of a turbine blade, fixed or movable, made of metal, in the aperture of a support made of metal, which is reliable, simple, and economical to put in place and to repair.

This object is achieved by the fact that this assembly comprises, between the foot and the aperture, at least one non-metallic film comprising polyamide, coated or impregnated with a polymer bonding agent.

According to a preferred embodiment, the film is arranged in such a manner that the bonding agent adheres to the foot of the blade. Alternatively, provision may be made for the film to adhere to the surface of the support aperture.

According to a preferred embodiment, the film comprises fibre glass, polytetrafluoroethylene, in particular Teflon (registered trademark), and/or polyamide, notably in the form of fibres, in particular of Kevlar or Nomex (registered trademarks).

Among the different possible solutions for the structure of the polymer film, the non-metallic film advantageously comprises a material made of synthetic fibres. There are, in fact, numerous types of synthetic fibres in existence which exhibit high wear resistance, as well as a low friction coefficient.

Advantageously, the bonding agent is thermo-polymerisable, which allows for the moment to be monitored at which this bonding agent takes, by placing the assembly in an autoclave brought to a minimum temperature for a predetermined period of time. By way of non-limitative example, the bonding agent is of the resin type, and comprises a phenol or polyurethane resin.

The assembly according to the present invention encompasses the situation in which the foot of the blade is lodged directly in the aperture, but likewise the situation in which the assembly additionally comprises at least one metallic foil mounted on the foot of the blade, said non-metallic film then being arranged between the foil and the aperture.

Preferably, the foot of the blade is made of titanium, of aluminium or of steel or of one of their alloys.

Likewise, preferably the blade support is made of titanium, of aluminium or of steel or of one of their alloys.

The present invention likewise relates to a turbine blower, comprising assemblies for the mounting of the foot of a blade according to one of the definitions given heretofore, characterised in that the blades are movable and the support is formed by the disk of the rotor.

The present invention also relates to a turbine compressor comprising assemblies for the mounting of the foot of a blade according to one of the definitions given heretofore, characterised in that the blades are movable and the support is formed by disk of the rotor.

The present invention also relates to a turbine compressor comprising assemblies for the mounting of the foot of a blade according to one of the definitions given heretofore, characterised in that the blades are movable and the support is formed by a flange.

Such compressors are, in particular, turbine compressors of the low-pressure type, but the invention can also relate to blades located at the intake of a high-pressure compressor, at the level of which the temperature attained does not prejudice the mechanical properties of any of the constituents of the wear resistance layer, namely the film and the bonding agent.

Finally, the present invention likewise relates to a turbine equipped with assemblies for the mounting of the foot of a blade according to one of the definitions given heretofore.

The invention will be readily understood and its advantages will become more apparent on reading the detailed description, which follows, of an embodiment of the invention represented by way of a non-limitative example.

The description refers to the appended drawings, in which:

FIG. 1 represents a partial transverse sectional view of a fan, showing the mounting of the foot of a blade in the rotor, the blade being subjected to the centrifugal forces of rotation, and

FIG. 2 represents a view similar to that of FIG. 1, according to a variant embodiment of the present invention.

FIG. 1 represents the mounting on the disk 10 of a blower or rotor of a blade 12, of which the foot 121 is located in one of the multiple apertures 101 of the disk 10.

More precisely, each aperture 101 has a shape which is approximately complementary to the shape of the foot 121 of the blade 12 to form a mounting of the dovetail type.

The apertures 101 are distributed radially and equidistantly over the entire length of the circumference of the disk 10, being open towards the outside.

As can be seen, the Figures show an enlarged portion of the transverse section of the disk 10, i.e. a section orthogonal to the axis of rotation of the fan, each foot 121 of a blade 12 having a symmetrical contour with two lateral walls 122, diverging in relation to one another from the body of the blade 12 in the direction of the free end of the foot 121 of the blade 12, as far as a base wall 124 approximately parallel to the axis of rotation and the periphery of the disk 10 and orthogonal to the principal orthogonal direction of the corresponding blade 12.

The apertures 101 have a similar shape to the lateral walls 102, inclined outwards from the circumference, in the direction of the interior portion of the disk 10 as far as a base wall 104.

The dimensions of the foot 121 of the blade 12 and of the blade 101 are such that, when the rotor 10 is at rest, the foot 121 is retained in the aperture 101, the base wall 124 of the foot 121 then being able to touch the base wall 104 of the aperture 101.

When the rotor 10 is operational during the working of the engine or turbine, the rotation of the rotor 10 about the central axis incurs a movement of the blades 12 in the radial direction outwards due to centrifugal forces, i.e. in the direction of the arrow 13 in FIG. 1. At this moment, the lateral walls 122 of the foot 121 of the blade 12 are supported against the lateral walls 102 of the aperture 101, which allows for the retention of the blade 12 in the interior of the aperture 101 to be assured, i.e. its connection to the disk 10.

At any change of the speed of rotation of the rotor 10, the sliding movement of the foot 121 of the blade, combined with the contact pressure of the foot 121 and the coefficient of the friction between the materials of the blade 12 and of the disk 10, generate shear forces simultaneously on the disk 10 and the blade 12, the one being displaced radially in relation to the other by 1 to several millimetres.

In particular, as can be derived from FIG. 1, when in operation a contact area exists, referred to as the bearing surface and subject to substantial forces, designated by the reference number 14, between the lateral wall 122 of the foot 121 and the lateral wall 102 of the aperture 101, as well as an area without contact, designated by the reference number 16, which is not subject to any mechanical contact stress during the rotation of the rotor formed from the disk 10.

According to the invention, the deterioration caused by fatigue and wear on the contact surfaces of the lateral walls 102 and 122 due to the relative movement between the foot 121 of the blade 12 and the aperture 101 of the rotor 10 is reduced by the use of a non-metallic film 20, which covers the whole outer surface of the foot 121.

More precisely, use is made of a film 20 which is advantageously formed from a wear-resistant fabric, such as a fabric from the CHEMFAB family of products from Saint-Gobain, manufactured based on glass fibres and/or aramide fibres, such as those known under the registered trademarks Nomex or Kevlar.

This film 20 adheres to the outer surface of the foot 121 with a bonding agent coating or impregnating the film 20, at least on the face of the film 20 before adhering, this bonding agent being preferably of the resin type, and advantageously a phenol or polyurethane resin.

For example, successful use has been made, for blades 12 made of titanium alloy and a disk 10 of titanium alloy, of a film 20 made of the pre-bonded wear-resistant fabric designated as Vespel ASB 0664 from Pont de Nemours (fabric composed of fibres of Nomex and Teflon—registered trademarks—pre-bonded with phenol resin), with, for the bonding agent, a phenol resin designated as Plyophen 23057 from Durez.

This film 20 has a first face coated with a layer of polytetrafluoroethylene for the lubricant, and a second face intended to be adhesively bonded, which has a good attachment and holding surface, the thickness of this film being of the order of some tenths of millimetres.

The adhesive is applied in a regular manner to the second face of the film, and this second face of the film 20 pre-treated with adhesive is then arranged on the lateral walls 122 and the base wall 124 of the foot 121 of each blade 12.

Preferably, the assembly formed by the foot of the blade 121, the resin, and the film 20 are placed under pressure during the adhesive bonding, i.e. the polymerisation of the resin. The pressure used is of the order of 7 to 14 MPa. This allows for good adhesion of the adhesive to be guaranteed over the whole of the surface, as well as the evacuation of the solvents.

It is during this period that polymerisation is carried out, which in this embodiment is carried out at 170° C. for a period of one hour.

A crushed film 20 is obtained, which adheres perfectly over the whole surface of the foot 121 of the blade 12, in such a way as to guarantee its presence in the area 14 after mounting, as shown in FIG. 1.

Advantageously, in the embodiment shown, the film 20 comprises on the surface opposite to that which is going to adhere to the foot 121, a layer of polytetrafluoroethylene (PTFE), which forms a lubricating surface which reduces the friction coefficient with the surface of the lateral walls 102 of the aperture 101 to a very significant degree, this friction coefficient possibly being as low as 0.1.

After the adhesive bonding, the foot 121 of the blade can be cleaned in order to remove the excess resin by blasting with glass beads.

Advantageously, following tests carried out with a mounting according to that from FIG. 1 and in accordance with the provisions of the embodiment described above, it proved possible to increase to a very substantial degree the service life of the mounting between the foot 121 and the aperture 101.

In fact, the result of these wear tests showed an increase in resistance without damage from 10,000 cycles with a traditional metallic cladding to 800,000 cycles with the film 20 from the embodiment.

It can, therefore, be understood that, in addition to the advantages in terms of ease of placement and rectification, the use according to the invention of a non-metallic wear-resistant film 20 provided with a layer of polytetrafluoroethylene provides considerably increased resistance to wear caused by friction.

Among the other advantages of the present invention, note should be taken of the possibility of avoiding changes to the structure of the material of the disk 10, which is sometimes encountered, for example, in the form of sweating, during the depositing of a metallic coating, particularly of the plasma type, or the removal of this deposit.

In addition to this, protection against wear by way of a non-metallic film 20 allows for easier non-destructive tests of the foot 121 of the blade. For example, recourse can be made to the technique of Foucault currents, which allows for the detection of defects (in particular micro-cracks or fissures) of small size (from about 0.1 mm).

Apart from this, with such an improvement it is possible to do away with the machining procedure referred to as “undercut”, which consists of broadening the aperture in the area of the emergence of the bearing surface 14, adjacent to the contact-free area 16, where the stress focal points are generally located.

Accordingly, the use of a technical fabric containing reinforcing fibres (of the aramide type) and teflon-treated fibres for the film 20 obtaining a lubrication effect, produces a reduction in the friction coefficient in the area 14, so reducing the forces engendered, which equates to improving mechanical resistance.

Advantageously, the film 20 is a technical fabric formed from a fibre glass and/or polyamide fibre material, advantageously comprising polytetrafluoroethylene.

The preceding arrangement makes provision for the placing of a film 20 over the whole surface of the foot 121 of each blade. It will be understood that this solution is easier and quicker, but in reality, in order to achieve the object of the invention, it is sufficient for the film 20 to cover the lateral walls 122 of the foot 121 in the contact area, i.e. the bearing surface 14.

This technique can likewise be applied, according to a variant, by adhesively bonding the non-metallic film 20 to the wall of the aperture 101 (not shown in the Figure).

According to another variant, not shown, a film 20 can at the same time be secured on the foot 121 of the blade 12 and on the wall of the blade 101.

It should be noted that the method according to the invention can readily be used during the initial mounting, but equally for carrying out a repair of the mounting between the foot 121 of a blade 12 and its aperture 101, whether this mounting was initially carried out in accordance with the invention or by having had recourse beforehand to a metallic wear-resistant coating.

In this latter case, the film 20 can be applied as a repair on the old metallic coating after a prior treatment consisting of blasting and cleaning said coating or after the complete removal of this old metallic coating.

Likewise, as shown in FIG. 2, according to a variant embodiment, the polymer film 20 is adhesively bonded onto a metallic foil 22, made, for example, from a super-alloy on a nickel base or of stainless steel.

In this Figure, the elements which are identical to those from FIG. 1 have retained the same reference symbols.

In this case, in order to implement the invention, use is made of a rigid core arranged in the interior of the foil 22 in order to avoid its possible deformation during the polymerisation under pressure of the adhesive.

The foil 22 is a cambered sheet with a U-shaped cross-section, the arms of which are divided into two parts so as to form an obtuse angle facing into the interior of the U. This shape approximates that of the foot 121 of the blade 121 in such a way that the end sections of the arms of the U of the foil cover the area 14 of contact between the foot 121 and the aperture 101.

In FIG. 2, the film 20 covers the whole outer surface of the foil 22.

Here too, by way of a variant, provision can be made for the film 20 to cover only the whole of the surface of the wall of the aperture 101, or at the same time all the outer surface of the foil 22 and all the surface of the wall of the aperture 101, or only an area comprising at least the area 14 of one, the other, or both of these surfaces.

The embodiment of this mounting variant is very close to that described previously in relation to FIG. 1, the only difference being the presence of the foil 22. Here again, it is understood that the film 20 can be placed, in accordance with the present invention, either on a new foil 22 without a coating, or on a foil 22 which has already been used and provided with coating (whether removing this traditional metallic coating or not), as well as for the repair of a part or all of the surface of the foil previously clad with such a film 20.

It can, therefore, be understood that the invention very easily, and according to several variants which give it great flexibility of application, allows for wear resistance results to be obtained which are absolutely excellent without changing the function of the mounting of the blades from the prior art whether during initial mounting or for the repair of a pre-existing mounting. 

1. Assembly for the mounting of the foot (121) of a blade (12), fixed or movable, of a turbomachine, made of metal, in the aperture (101) of a support made of metal, characterised in that it comprises, between the foot (121) and the aperture (101), at least one non-metallic film (20) comprising polyamide, coated or impregnated with a polymer adhesive.
 2. Assembly according to the preceding claim, characterised in that the film (20) further comprises fibre glass and/or polytetrafluoroethylene.
 3. Assembly according to claim 1 or 2, characterised in that the film (20) comprises a fabric made of synthetic fibres.
 4. Assembly according to any one of the preceding claims, characterised in that the adhesive is thermo-polymerisable.
 5. Assembly according to claim 4, characterised in that the adhesive comprises a phenolic or polyurethane resin.
 6. Assembly according to any one of the preceding claims, characterised in that it further comprises at least one metallic foil (22) mounted on the foot of the blade, said non-metallic film (20) being arranged between the foil (22) and the aperture (101).
 7. Assembly according to any one of the preceding claims, characterised in that the foot (121) of the blade (12) is made of titanium, of aluminium or of steel or of one of their alloys.
 8. Turbomachine fan comprising assemblies for the mounting of the foot (121) of a blade (12) according to any one of the preceding claims, characterised in that the blades (12) are movable and the support is formed by the disk (10) of the rotor.
 9. Turbomachine compressor comprising assemblies for the mounting of the foot of a blade according to any one of claims 1 to 7, characterised in that the blades (12) are movable and the support is formed by the disk (10) of the rotor.
 10. Turbomachine compressor comprising assemblies for the mounting of the foot of a blade according to any one of claims 1 to 7, characterised in that the blades are fixed and the support is formed by a flange.
 11. Turbomachine equipped with assemblies for the mounting of the foot of a blade according to any one of claims 1 to
 7. 12. Method for the mounting of the foot of a turbine blade (12) made of metal, fixed or movable, in the aperture (101) of a metal support (10), characterised in that it comprises the following steps: a) Arranged between the foot (121) and the aperture (101) is a non-metallic film (20) comprising polyamide, coated or impregnated with a polymer adhesive; and b) The adhesive must be applied in such a way that the film (20) adheres to the foot (121) of the blade (12) and/or to the surface of the aperture (101).
 13. Mounting method according to claim 12, characterised in that the adhesive is thermo-polymerisable, and in that in the course of step b), the assembly comprising at least the foot (121) of the blade, the support (10), and the film (20) is placed in an autoclave brought to a temperature which will allow the adhesive to take.
 14. Mounting method according to claim 12 or 13, characterised in that the film (20) is arranged in such a way that the adhesive adheres to the foot (121) of the blade.
 15. Mounting method according to either of claims 12 or 13 characterised in that, during step a), the foot of the blade is clad with a metallic foil (22), said film (20) being arranged between the foil (22) and the aperture (121).
 16. Mounting method according to any one of claims 12 to 15, characterised in that the film (20) further comprises fibre glass and/or polytetrafluoroethylene.
 17. Mounting method according to any one of claims 12 to 15, characterised in that the film (20) comprises a fabric made of synthetic fibres. 